1. Field of the Invention
The present invention relates to a gateway apparatus that can relay a packet between a plurality of networks.
2. Description of the Related Art
There is known a system called “sensor network” or “home network,” which can be used inside and outside houses, factories and buildings, to manage, control and operate various objects, equipment and machines. One example of such system can be found in “ECHONET SPECIFICATION, Part 9, ECHONET, Gateway Apparatus Specification, Version 321” (ECHONET consortium, Oct. 13, 2005; http://www.echonet.gr.jp/8_kikaku/spec/pdf_v3.21/SpecVer321—09.pdf). This ECHONET SPECIFICATION defines an industry standard for home networks, which is referred to as ECHONET Gateway Apparatus Specification. In general, it is unusual that a system including sensors and control devices operates independently of other systems. In other words, a system (referred to as “subject system”) generally operates in cooperation with other systems (referred to as “external system”). In order to cooperate with an external system, a gateway apparatus is provided at a connection between the subject system and external system. The gateway apparatus relays data between these two systems. The gateway apparatus often has a system security function to provide a secured connection between the subject and external systems. The gateway apparatus may also have an adjusting function to provide a better matching (smooth connection) between the two systems.